In an automotive vehicle, friction clutches of automatic transmissions are known in which the clutch pedal is absent, the clutch unit being actuated via an electric motor controlled as a function of the values of certain operating parameters of the vehicle. These parameters of course include the rotational velocities both upstream and downstream of the clutch. Measurement of these velocities has hitherto been obtained by the use of certain of the gear wheels in the gearbox, together with the engine crank shaft, which involves making comparatively expensive modifications to the gearbox and the engine casing. This concept is particularly well illustrated by the clutch unit disclosed in an article in the periodical "Argus Automobile" of Apr. 21, 1988, or in an article in the issue of "Popular Science" for March 1988.
It will be realised that the arrangement of the necessary sensors calls for additional mechanical operations during manufacture and also for some adaptation in the mounting of the gearbox and engine casings.